The application of liquid coating materials to large objects such as automotive and other vehicle bodies has conventionally been accomplished in spray booths having an elongated tunnel-like construction formed with an inlet for the ingress of the vehicle body, a coating application area, a curing or drying area in some designs, and an outlet for the egress of the vehicle body. In many systems, "conditioned" air, i.e., humidified and filtered air, is introduced by a blower or feed fan into a plenum chamber at the top of the spray booth and then directed downwardly toward the vehicle body moving through the booth. The conditioned air picks up oversprayed coating material within the booth interior and this air-entrained oversprayed material is drawn downwardly through the floor of the booth by an exhaust fan. Filters are located at the bottom of the booth to capture the oversprayed material, and the resulting filtered or clean air is withdrawn from the booth and either exhausted to atmosphere or recirculated within the system for reuse.
The coating material in most common use for vehicles such as automobiles is a high solids resinous paint material which contains a relatively high percentage of liquid solvent components to facilitate atomization of the resinous material. The problems attendant to the recovery of oversprayed, resinous paint material have been well documented and present a continuing environmental problem for the coating and finishing industry. See, for example, U.S. Pat. Nos. 4,247,591 to Cobbs et al and 4,553,701 to Rehman et al.
As an alternative to solvent-based liquid paint material, the use of powder coating material has been proposed for application to vehicle bodies and other relatively large objects. In the practice of powder coating, a powdered resin is applied to the substrate and then the substrate and powder are heated so that the powder melts and when subsequently cooled, forms a solid continuous coating on the substrate. In most powder spraying applications, an electrostatic charge is applied to the sprayed powder which is directed toward a grounded object to be coated so as to increase the quantity of powder which attaches to the substrate and to assist in retaining the powder on the substrate.
As disclosed, for example, in U.S. Pat. No. 3,847,118, the application of powder material onto large objects such as automotive or other vehicle bodies has been performed in a spray booth which provides a control area wherein oversprayed powder which is not deposited on the vehicle body can be collected. Containment of the oversprayed powder within the booth in apparatus of this type is aided by an exhaust system which creates a negative pressure within the booth and causes the oversprayed powder to be drawn through the booth and into a powder collection and recovery system. The recovered oversprayed powder can be saved for future use or immediately recycled to powder dispensers associated with the spray booth.
It has been observed that the application of powder coating material onto large objects such as automotive bodies presents a number of difficulties, many of which can be attributed to the large physical size of the spray booth and the large quantity of powder coating material required to coat vehicle bodies. Many powder coating systems do not have the capacity to collect and recover the large quantity of oversprayed powder obtained from coating a vehicle body. Additionally, access to the various components of the powder collection and recovery system, particularly the powder filters, for maintenance and/or replacement is difficult in many prior powder coating booth designs. This is of particular concern in a spray booth for vehicle bodies wherein a large quantity of powder material must be collected and recovered.